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| LDP Concept | Fedora Concept | LDP Interaction Modes | Constraints on Content |
|---|---|---|---|
| LDPC | Object | LDPC, LDP-RS | RDF, must contain LDP membership triples, subjects must be repository objects, subjects must be the URI of the object |
| LDP-NR | Datastream | LDPR for properties, LDP-NR for bitstream | none |
| LDP-RS-NC | - | - | - |
The issue at hand is whether Fedora should support the LDP construct of an RDF source that is not also a container (LDP-RS-NC), and how such an resource in LDP would map to a concept in Fedora.
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| LDP Concept | Fedora Concept | LDP Interaction Modes | Constraints on Content |
|---|---|---|---|
| LDPC | Object | LDPC, LDP-RS | RDF, must contain LDP membership triples, subjects must be repository objects, subjects must be the URI of the object |
| LDP-NR | Datastream | LDPR for properties, LDP-NR for bitstream | none |
| LDP-RS-NC | - | - | - |
Note that this proposal maintains the current behaviour in that LDP-RS-NC is not supported.
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| LDP Concept | Fedora Concept | LDP Interaction Modes | Constraints on Content |
|---|---|---|---|
| LDPC | Object | LDPC, LDP-RS | RDF, must contain LDP membership triples, subjects must be repository objects, subjects must be the URI of the object |
| LDP-NR | Datastream | LDPR for properties, LDP-NR for bitstream | none |
| LDP-RS-NC | DatastreamSpecial datastream | LDPR, LDP-RS | RDF |
Note that 'Objects' objects in the Fedora model map to the LDPC interaction model, while 'Datastreams' in Fedora any resource that provides a datastream's properties and the new special type of datastream introduced here both map to the LDPR interaction model. The distinguishing factor of a Fedora object, as exposed by LDP, is that it is a container. The distinguishing factor of a special datastream, exposed in LDP, is that it is not a container (i.e. it is a leaf node in the LDP model).
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- The Fedora object model does not change at all with this proposal
- The LDP-RS-NCs created by Fedora may contain arbitrary RDF. This is a consequence of their 'datastream' nature, in that their content is largely opaque to the Fedora model. They are blobs, so there is no inherent need to constrain their content other than to verify that they contain RDF as implied by an LDP-RS.
- No inherent restriction on allowable subjects, predicates, or objects in the triples
- No inherent restriction on constructs such as blank nodes
- This implies an unknown but high cost for implementation.
- The LDP-RS-NCs created to by Fedora may be 'pure' in that they are logically unmodified from client requests. Again, this is due to their nature as an opaque datastream as far as the fedora model is concerned.
- No server managed triples are added by Fedora
- The LDP-RS-NCs benefit from the LDP-RS interaction model as defined by LDP on these resources:
- Retrieve triples in specified representation (xml, turtle, ntriples, etc); as per LDP spec text/turtle and application/ld+json representations are always available.
- SPARQL Update semantics (PATCH)
- Interpretation of relative URIs in RDF content as per the LDP spec (for example, allowing null relative URIs "<>" to refer to the to-be-created resource URI)
- This also implies an unknown but high cost for implementation.
If it helps, this proposal can be also be conceptualized as a kind of 'service' provided on top of a datastream to provide an enhanced RDF CRUD API that neatly maps to an LDP concept that Fedora does not currently support, but most LDP servers do.
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| LDP Concept | Fedora Concept | LDP Interaction Modes | Constraints on Content |
|---|---|---|---|
| LDPC | Object | LDPC, LDP-RS | RDF, must contain LDP membership triples, subjects must be repository objects, subjects must be the URI of the object |
| LDP-NR | Datastream | LDPR for properties, LDP-NR for bitstream | none |
| LDP-RS-NC | Object | LDPR, LDP-RS | RDF, subjects must be repository objects, subjects must be the URI of the object |
Note that 'Objects' objects in the Fedora model map to the LDP-RS interaction model, while 'Datastreams' datastreams in Fedora map to the LDPR and LDP-NR interaction model. The distinguishing factor of a Fedora object, as exposed by LDP, is that is an RDF source. The distinguishing factor of a datastream is that it is a non-RDF sourcemodels.
Proposal: LDPRs as "Pointlike objects" with no constraints on RDF statements.
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| LDP Concept | Fedora Concept | LDP Interaction Modes | Constraints on Content |
|---|---|---|---|
| LDPC | Object | LDPC, LDP-RS | RDF, must contain LDP membership triples |
| LDP-NR | Datastream | LDPR for properties, LDP-NR for bitstream | none |
| LDP-RS-NC | Object | LDPR, LDP-RS | RDF |
Note that 'Objects' in the Fedora model map to the LDP-RS interaction model, while 'Datastreams' in Fedora map to the LDP-NR interaction model. The distinguishing factor of a Fedora object, as exposed by LDP, is that is an RDF source. The distinguishing factor of the resource that provides a datastream's bitstream is that it is a non-RDF source.
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